A portable terminal, such as a smart phone, may be said to be one of the most important personal devices due to its extensible functionality. Touch window glass is installed on the front surface of the terminal. In general, such touch window glass has a plane (two dimensions) shape. Recently, a variety of types of functions are assigned to a smart phone, and a smart phone including touch window glass in part of which a curved surface has been formed in order to increase the satisfaction of the functions is released.
In a current portable terminal having curved glass, at least one part of glass may be formed into a curved surface with respect to a single axis. Glass at least one part of which has been formed into a curved surface on the basis of a single axis as described above is called curved glass or 3D glass. Such 3D glass is fabricated in a high temperature atmosphere. For example, glass of a flat panel shape is put between an upper mold and a lower mold including a cavity having a curved surface shape corresponding to the curved surface shape of touch window glass and is then exposed to a high temperature atmosphere of 700° C. or more, for example, thereby forming 3D touch window glass having the curved surface shape corresponding to the cavity between the upper and lower molds.
Furthermore, the back of curved glass installed on the front surface of a smart phone includes a touch pad part for implementing a touch pad function for detecting a touched point based on a change of a current value or the detection of contact pressure. Such a touch pad function part may include, for example, an ITO deposition layer and a silver paste layer for electrically connecting the ITO deposition layer and a printed circuit board (PCB).
Touch window glass is basically transparent, but printing having a predetermined shape is performed on the back of the touch window glass so that an electronic part installed on the back of the touch window glass is not exposed at the front. In this case, in the aforementioned 2D glass, printing may be performed relatively simply because it is performed on a plane. However, it is not easy to form a printing layer on recent 3D glass from the view point of the stereoscopic structure of 3D glass.
A conventional printing process is described below. As shown in FIG. 1, after 2D glass, that is, plane glass, is processed as step S10, the plane glass is processed into 3D glass, that is, curved glass at step S14. Furthermore, printing having a specific pattern is performed on one side of the 3D glass processed to have a curved surface. However, there are many difficulties in printing the 3D glass having the curved surface. Furthermore, the specific pattern is printed on one side of the curved glass using a commercialized technology, for example, a printing apparatus having a complicated structure.
Furthermore, in a technology disclosed in Korean Patent No. 10-1449363 issued to the present applicant, 3D-processed glass is planarized using a specific force (suction force) and then printed. In this case, since printing is performed on glass after 3D processing is performed on the glass, there is a difficulty in that a specific apparatus is required to make curved glass a flat panel.
Furthermore, in the Korean Patent, printing is performed after touch window glass has been processed into 3D glass. Furthermore, in all conventional technologies, printing is performed on touch window glass for a portable terminal after a glass forming process performed in a high temperature atmosphere is completed and the formed glass is cooled at room temperature. Printing is performed after 3D glass for a smart phone or a portable terminal is fully formed as described above because the 3D glass is formed in a high temperature atmosphere. The reason for this is that a printed portion is changed if printing is first performed and the printed plane (2D) glass is then processed in a high temperature atmosphere.